The invention relates to the field of satellite communications, more generally known as SATCOM. It more particularly relates to a parabolic antenna positioner to allow communication with a satellite, said positioner in particular being intended to be placed on a moving carrier.
Different types of parabolic antenna positioners currently exist to make it possible to establish a communication with a satellite, these positioners either being stationary relative to the ground, or mobile when they are placed on moving carriers.
Application WO 2009/033085 and U.S. Pat. No. 6,285,338 for example describe positioners of the Elevation over Azimuth type. These positioners include two axes of rotation, one making it possible to vary the azimuth of the parabolic antenna, i.e. the horizontal angle between the direction of the parabolic antenna and a reference direction generally corresponding to geographical north, and the other making it possible to vary the elevation of the parabolic antenna, the vertical angle between the direction of the parabolic antenna and the reference direction (geographical north). Such positioners do, however, have the drawback of having a singular point (better known under the name “keyhole”) at the vertical, i.e. the zenith. The notion of keyhole, well known by those skilled in the art, designates a point where the communication between the satellite and the parabolic antenna is difficult, or even impossible, due to the dynamic positioning constraints of the parabolic antenna in the direction of the keyhole. In the particular case of an Elevation over Azimuth positioner, the Azimuth rotation of the parabolic antenna reaches very significant, even infinite, speeds of rotation, upon passage near the keyhole at the vertical with the result that the antenna finds it very difficult to align itself with a satellite situated at the vertical. This communication difficulty is problematic if the positioner is on a moving carrier due to the dynamics that the movement of the carrier gives to the parabolic antenna. Consequently, it is difficult to use such positioners in land areas where the satellites are situated at the vertical of the parabolic antennas, in particular in the equatorial areas.
Applications US 2002/0030631, GB 735 359 and US 2003/0141420 describe XY-type positioners, allowing the parabolic antenna to rotate along two perpendicular horizontal axes X and Y, and for which no keyhole appears at the vertical. These known XY-type positioners do, however, have the drawback of not being balanced or of only being able to be balanced by adding a counterweight, which significantly increases the total mass of the positioners. In fact, to be balanced, an XY-type positioner must be such that the center of gravity of its load, in particular the parabolic antenna, is situated on the axes of rotation X and Y of the load. However, the weight of the load is generally distributed more on one axis than the other and counterweights must therefore be added to offset the imbalance. Such weight overload and imbalance characteristics are not acceptable for a parabolic antenna positioner intended to be placed on a moving carrier, because they damage the dynamic performance of the positioner, and oppose the lightness requirements necessary in certain applications, such as in the aeronautics field.
Lastly, application CA 1 236 211 describes another type of parabolic antenna positioner including three axes of rotation to make it possible to orient, the parabolic antenna in all possible directions toward the satellite. Such a positioner does not have any keyhole, but is very complex to make, very bulky and very expensive.